The above-named professional personnel propose to collaborate with other members of the Children's Cancer Study Group as well as with other members of other cooperative cancer study groups, in research on leukemia, malignant solid tumors and closely related disorders in children. The chief purpose of this study group is to cooperate in research on malignant diseases in children and, in particular, to study factors which may cause or influence cancer and to develop, evaluate and improve methods of diagnosis and treatment of malignant diseases in children. Special emphasis will be placed on the study of new combinations and new schedules of already established chemotherapeutic agents as well as on the evaluation of new anti-cancer agents and new modalities of therapy. A particular interest of the Principal Investigator is histiocytosis X and a new protocol is being drafted. In this regard, it should be emphasized that of the two publications re histiocytosis, resulting from our Group's Study 611, which appeared in the August issue of the Journal of Pediatrics, more than 800 requests for reprints have been received from all over the world.